Biomedical Engineering Reference
In-Depth Information
Apatite phase formed
Fig. 2. Cross section of the apatite-containing surface layer formed, SEM (Engqvist et al,
2004)
Ion release measured by atomic absorption spectrometry
The results of Ca and Al determination in the solution during the hydration process of the
Ca-aluminate based material are presented in Table 6.
Ion tested 1h, ppm 24 hrs, ppm 7 days, ppm
28 days, ppm
Ca 66 64 44
50 (70)
Al 11.4 9.3 9.6
8.6 (1.2)
Table 6. Ca and Al dissolution during hardening of the Ca-aluminate material, (The 1h
testing at 28 days within brackets)
The release of metal ions in water was below 5x10
-2
ppm/(mm
2
material) for aluminium and
below 30x10
-2
ppm/(mm
2
material) for calcium, whereas somewhat higher aluminium
content was measured in artificial saliva. The ion concentrations detected are generally not
time-dependent during hydration. After the initial hydration time the ion concentration
(molar) is determined by the solubility product of the phases formed (katoite = 5x10
-26
and
gibbsite = 3x10
-24
). Since the concentration of Ca in saliva is higher than what is obtained in
the non-physiological aqueous solution (distilled water), it can be assumed that the filling
material releases very limited amounts of Ca or Al once the material has hardened. The
presence of Ca in saliva will decrease the solubility tendency of the calcium-aluminate-
hydrate phases.
Based on a search in the literature, the FAO/WHO Joint Expert Committee on Food
Additives (JECFA) has provided a provisional figure for tolerable weekly aluminium intake
of 7 mg/kg body weight. This corresponds to 1 mg/kg /day. The daily intake of aluminium
via digestion/food is approximately 5 mg per day. For calcium the NIH Consensus
Development Conference on Optimal Calcium Intake recommended an intake in the range
800 mg/day for young children to 1000 - 1500 mg/day for adults depending on gender and
age. For many people there is a need to supply additional calcium in order to stay healthy.
The ion concentrations measured and the amounts of Ca and Al released are far below the
concentrations of the elements produced from food intake and should therefore not pose
any safety concerns at all.
